Determining Logic Trunked Radio (LTR) Frequency Position

 

The information here is intended to help you determine the correct order of frequencies for an LTR system.  There can be anywhere from 2 to 20 frequencies in an LTR system.  LTR uses “home” repeaters.  A channel in an LTR system will monitor the home repeater to determine what repeater to transmit on and listen to.  If that home repeater is available, it will be used, otherwise, a random available repeater will be selected.  For a very technical explanation of LTR, please visit here.

 

It is important to have the LTR system’s frequencies programmed in the correct order for a scanner, like the Uniden BC780XLT, to track channels on the trunked system.  Perhaps the hardest part of this process is determining what frequencies are used by the system.  FCC records may be helpful, but do not count on all frequencies being under the same record or call letters. 

 

The system I was trying to figure out, that led to this article, was found when someone heard a police department on a single frequency that was being used in an LTR system.  I looked up the frequency in FCC records, which led to 20 frequencies that were associated with the frequency.  I first started by programming the 20 frequencies into the 780 in ascending order.  After listening a while, it was obvious some of the frequencies were not part of the same LTR system, or any LTR system.  Others were obviously not in the right channel because the scanner would not track properly. After figuring out 4 or 5 of the channels, and sharing them online, someone else with an inside source sent a complete list of all 20 frequencies in the system, all in the right order! That certainly made things easier.  Chances are you won’t be that lucky, but there are many systems already listed in detail at places like www.trunkedradio.net, so check there first.

 

Before too much detail, that may not be necessary, keep in mind that it is common for a 5 frequency system to use the channels 1, 5, 9, 13, and 17.  If you know you are trying to figure out a 5 frequency LTR system, start with that and see how it goes. You may not need to do anything else.  Note however, that the frequencies may not be in ascending order, so there could be more to be determined.  Also note that when programming a scanner, like the BC780XLT, the channel numbers are relative to the scan bank, in which you are programming them.  For example, on the BC780XLT, if you’re programming a common 5 frequency LTR system into bank 3, they should be programmed into scanner channel numbers 101, 105, 109, 113, and 117.

 

OK, down to business.  A lot can be determined by sitting on a frequency in the scanner’s trunked mode.  For the BC780XLT, make sure you program the bank for LTR by following these steps.

Press the Menu key

Press 3 for Trunk Data

Press the number of the bank you want to make LTR

Press Enter on Trunk Type

Press 8 for LTR

Press Manual to return to manual mode

 

As you program in frequencies, make sure you hold the Trunk key, until “L” is displayed.

 

Once you have frequencies programmed in, you can press the Manual key, or Up Arrow and Down Arrow keys to move through the frequencies. Us the Trunk key to toggle Trunk Tracking mode on and off.  When there is activity on a frequency, something like this 1-01-034 will be displayed.  The first “1” indicates the area code for the system.  The area code will be either 0 or 1.  If you are seeing mixed area codes on a collection of frequencies then, make a list of what frequencies had what area codes on them.  You can then separate those groups of frequencies from each other, because they represent two different LTR systems.  The next set of digits, is the home repeater, and will be between 01 and 20.  The last set of digits is the ID for the channel (also know as group or talkgroup).

 

The home repeater digits are very helpful in determining what position a frequency is.  If you consistently see the same home channel on a frequency, then chances are that is the channel where the frequency belongs.  For example, if you have 451.275 programmed into scanner channel 13, but you usually see the home repeater #-01-### displayed when sitting on that frequency, then that frequency should be moved to scanner channel 1.  Of course, if you’re talking about a 20 frequency system this will take some time.

 

One way to speed things up is to program the same frequency in channels 1 through 20, enter trunk mode, and scan/search until activity is found. Then quickly switch out of trunk mode. The scanner channel that you landed on should be the proper channel number for that frequency.

 

If you’re trying to figure out a business (the most common LTR users) LTR system, then listening after peak business hours may make a difference.  If the system has an automatic call letter ID by Morse code, they often show up as #-##-253.  If the system is not busy, then the home channel from those IDs may be easier to figure out.  On the system I mentioned earlier, each home repeater is automatically ID’d regularly with the #-##-253.

 

I’m no expert on LTR, but hope this info from my experiences and a little bit of knowledge of LTR, will be helpful in figuring out undocumented LTR systems.  If you have any tips of your own that you think other might find helpful, please let me know, and I’ll try to work them in here.

 

Ben Saladino – Return to Scanning the Dallas/Fort Worth Area